/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/****************************************************************************
 * libc/stdio/lib_libfread.c
 *
 *   Copyright (C) 2007-2009, 2011-2014 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <tinyara/config.h>

#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>

#include "lib_internal.h"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/****************************************************************************
 * Private Type Declarations
 ****************************************************************************/

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

/****************************************************************************
 * Global Constant Data
 ****************************************************************************/

/****************************************************************************
 * Global Variables
 ****************************************************************************/

/****************************************************************************
 * Private Constant Data
 ****************************************************************************/

/****************************************************************************
 * Private Variables
 ****************************************************************************/

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: lib_fread
 ****************************************************************************/

ssize_t lib_fread(FAR void *ptr, size_t count, FAR FILE *stream)
{
	unsigned char *dest = (unsigned char *)ptr;
	ssize_t bytes_read;
#if CONFIG_STDIO_BUFFER_SIZE > 0
	int ret;
#endif

	/* Make sure that reading from this stream is allowed */

	if (!stream || (stream->fs_oflags & O_RDOK) == 0) {
		set_errno(EBADF);
		bytes_read = -1;
	} else {
		/* The stream must be stable until we complete the read */

		lib_take_semaphore(stream);

#if CONFIG_NUNGET_CHARS > 0
		/* First, re-read any previously ungotten characters */

		while ((stream->fs_nungotten > 0) && (count > 0)) {
			/* Decrement the count of ungotten bytes to get an index */

			stream->fs_nungotten--;

			/* Return the last ungotten byte */

			*dest++ = stream->fs_ungotten[stream->fs_nungotten];

			/* That's one less byte that we have to read */

			count--;
		}
#endif

#if CONFIG_STDIO_BUFFER_SIZE > 0
		/* If the buffer is currently being used for write access, then
		 * flush all of the buffered write data.  We do not support concurrent
		 * buffered read/write access.
		 */

		ret = lib_wrflush(stream);
		if (ret < 0) {
			lib_give_semaphore(stream);
			return ret;
		}

		/* Now get any other needed chars from the buffer or the file. */

		while (count > 0) {
			/* Is there readable data in the buffer? */

			while ((count > 0) && (stream->fs_bufpos < stream->fs_bufread)) {
				/* Yes, copy a byte into the user buffer */

				*dest++ = *stream->fs_bufpos++;
				count--;
			}

			/* The buffer is empty OR we have already supplied the number of
			 * bytes requested in the read.  Check if we need to read
			 * more from the file.
			 */

			if (count > 0) {
				size_t buffer_available;

				/* We need to read more data into the buffer from the file */

				/* Mark the buffer empty */

				stream->fs_bufpos = stream->fs_bufread = stream->fs_bufstart;

				/* How much space is available in the buffer? */

				buffer_available = stream->fs_bufend - stream->fs_bufread;

				/* Will the number of bytes that we need to read fit into
				 * the buffer space that is available? If the read size is
				 * larger than the buffer, then read some of the data
				 * directly into the user's buffer.
				 */

				if (count > buffer_available) {
					bytes_read = read(stream->fs_fd, dest, count);
					if (bytes_read < 0) {
						/* An error occurred on the read.  The error code is
						 * in the 'errno' variable.
						 */

						goto errout_with_errno;
					} else if (bytes_read == 0) {
						/* We are at the end of the file.  But we may already
						 * have buffered data.  In that case, we will report
						 * the EOF indication later.
						 */

						goto shortread;
					} else {
						/* Some bytes were read. Adjust the dest pointer */

						dest += bytes_read;

						/* Were all of the requested bytes read? */

						if ((size_t)bytes_read < count) {
							/* No.  We must be at the end of file. */

							goto shortread;
						} else {
							/* Yes.  We are done. */

							count = 0;
						}
					}
				} else {
					/* The number of bytes required to satisfy the read
					 * is less than or equal to the size of the buffer
					 * space that we have left. Read as much as we can
					 * into the buffer.
					 */

					bytes_read = read(stream->fs_fd, stream->fs_bufread, buffer_available);
					if (bytes_read < 0) {
						/* An error occurred on the read.  The error code is
						 * in the 'errno' variable.
						 */

						goto errout_with_errno;
					} else if (bytes_read == 0) {
						/* We are at the end of the file.  But we may already
						 * have buffered data.  In that case, we will report
						 * the EOF indication later.
						 */

						goto shortread;
					} else {
						/* Some bytes were read */

						stream->fs_bufread += bytes_read;
					}
				}
			}
		}
#else
		/* Now get any other needed chars from the file. */

		while (count > 0) {
			bytes_read = read(stream->fs_fd, dest, count);
			if (bytes_read < 0) {
				/* An error occurred on the read.  The error code is
				 * in the 'errno' variable.
				 */

				goto errout_with_errno;
			} else if (bytes_read == 0) {
				/* We are at the end of the file.  But we may already
				 * have buffered data.  In that case, we will report
				 * the EOF indication later.
				 */

				break;
			} else {
				dest += bytes_read;
				count -= bytes_read;
			}
		}
#endif
		/* Here after a successful (but perhaps short) read */

#if CONFIG_STDIO_BUFFER_SIZE > 0
shortread:
#endif
		bytes_read = dest - (unsigned char *)ptr;

		/* Set or clear the EOF indicator.  If we get here because of a
		 * short read and the total number of* bytes read is zero, then
		 * we must be at the end-of-file.
		 */

		if (bytes_read > 0) {
			stream->fs_flags &= ~__FS_FLAG_EOF;
		} else {
			stream->fs_flags |= __FS_FLAG_EOF;
		}

		lib_give_semaphore(stream);
	}

	return bytes_read;

	/* Error exits */

errout_with_errno:
	stream->fs_flags |= __FS_FLAG_ERROR;
	lib_give_semaphore(stream);
	return -get_errno();
}
